Classic Zucchini Casserole

This classic zucchini casserole transforms humble summer squash into a rich, comforting dish that’s perfect for using up your garden’s bounty. Layers of tender zucchini meld with creamy cheese sauce and savory herbs to create a satisfying side dish that pairs beautifully with everything from grilled chicken to holiday roasts. Despite its impressive appearance, this easy casserole requires just basic prep work and bakes hands-free while you prepare the rest of your meal.

Recipe Details

Prep Time: 20 mins
Cook Time: 45 mins
Total Time: 65 mins
Servings: 8
Difficulty: Easy

Ingredients

For the Zucchini Base:

• 3 lbs medium zucchini (about 6-8 zucchini), sliced into 1/4-inch rounds
• 2 teaspoons kosher salt
• 2 tablespoons olive oil
• 1 large yellow onion, thinly sliced
• 3 cloves garlic, minced
• 1 teaspoon dried oregano
• 1/2 teaspoon dried thyme
• 1/4 teaspoon black pepper

For the Cheese Sauce:

• 3 tablespoons butter
• 3 tablespoons all-purpose flour
• 1 1/2 cups whole milk, warmed
• 1 cup sharp cheddar cheese, freshly grated
• 1/2 cup Gruyère cheese, freshly grated
• 1/4 cup Parmesan cheese, freshly grated
• 1/2 teaspoon salt
• 1/4 teaspoon white pepper
• Pinch of nutmeg

For the Topping:

• 1/2 cup panko breadcrumbs
• 1/4 cup Parmesan cheese, freshly grated
• 2 tablespoons butter, melted
• 1 tablespoon fresh parsley, chopped

Instructions

1. Prepare the zucchini: Slice zucchini into uniform 1/4-inch rounds using a sharp knife or mandoline. Place slices in a large colander, toss with kosher salt, and let drain for 15 minutes to remove excess moisture.
2. Preheat and prep: Preheat oven to 375°F. Butter a 9×13-inch baking dish and set aside. After 15 minutes, pat zucchini slices thoroughly dry with paper towels to ensure the casserole won’t be watery.
3. Sauté aromatics: Heat olive oil in a large skillet over medium heat. Add sliced onions and cook for 5-6 minutes until softened and lightly golden. Add minced garlic, oregano, and thyme, cooking for another 30 seconds until fragrant.
4. Make cheese sauce base: In a medium saucepan, melt butter over medium heat. Whisk in flour and cook for 1-2 minutes, stirring constantly, until mixture turns light golden and smells nutty.
5. Build the sauce: Gradually whisk in warmed milk, ensuring no lumps form. Continue cooking, whisking frequently, for 3-4 minutes until sauce thickens enough to coat the back of a spoon.
6. Add cheeses: Remove saucepan from heat and gradually stir in cheddar, Gruyère, and Parmesan cheeses until completely melted and smooth. Season with salt, white pepper, and nutmeg. The sauce should be creamy and pourable.
7. Layer the casserole: Arrange half the zucchini slices in the prepared baking dish, slightly overlapping. Spread the sautéed onion mixture evenly over zucchini, then top with remaining zucchini slices in an overlapping pattern.
8. Add sauce and topping: Pour cheese sauce evenly over the layered zucchini, using a spoon to ensure it reaches all corners. Combine panko breadcrumbs, Parmesan, melted butter, and parsley in a small bowl, then sprinkle over the entire surface.
9. Bake to perfection: Cover with foil and bake for 30 minutes. Remove foil and continue baking for 12-15 minutes until top is golden brown and bubbling around the edges. A knife inserted in center should slide through easily.
10. Rest before serving: Let the classic zucchini casserole rest for 10 minutes before cutting. This allows the layers to set properly and makes serving much easier.

Tips for Success

Moisture control is crucial: Don’t skip the salting and draining step for the zucchini. This prevents a watery casserole and ensures the cheese sauce maintains its creamy texture throughout baking.

Slice consistency matters: Uniform 1/4-inch slices ensure even cooking. Thicker pieces may remain undercooked while thinner ones become mushy.

Cheese sauce troubleshooting: If your sauce becomes lumpy, remove from heat and whisk vigorously. For stubborn lumps, strain the sauce through a fine-mesh sieve before adding to the casserole.

Visual cues for doneness: The casserole is ready when the top is golden brown, edges are bubbling, and a knife slides through the center layers without resistance.

Recipe Variations

Mediterranean style: Replace herbs with fresh basil and oregano, add a layer of sliced tomatoes, and substitute feta and mozzarella for some of the cheeses in this classic zucchini casserole.

Protein-packed version: Add 1 cup of cooked, crumbled Italian sausage or diced ham between the zucchini layers for a hearty main dish option.

Lighter alternative: Use half-and-half instead of whole milk and reduce cheese quantities by one-third. The casserole will still be delicious but with fewer calories.

Herb garden variation: Replace dried herbs with 2 tablespoons fresh herbs like basil, thyme, and oregano for a more vibrant flavor profile.

Storage Instructions

Store leftover classic zucchini casserole covered in the refrigerator for up to 4 days. The flavors actually improve after the first day as they have time to meld together.

Reheat individual portions in the microwave for 1-2 minutes, or warm larger portions in a 350°F oven for 15-20 minutes until heated through. Cover with foil to prevent the top from over-browning during reheating.

For longer storage, this casserole freezes well for up to 3 months. Thaw overnight in the refrigerator before reheating using the oven method above.

Make-Ahead Strategy

This classic zucchini casserole is perfect for advance preparation. Assemble the entire dish up to 24 hours ahead, cover tightly, and refrigerate. Add 5-10 minutes to the covered baking time since you’re starting with a cold dish.

You can also prepare components separately: slice and salt zucchini, make cheese sauce, and prepare topping up to 2 days ahead. Store each component separately and assemble just before baking.

Nutritional Highlights

Zucchini provides excellent nutritional value while keeping calories relatively low. This versatile vegetable contributes vitamin C, potassium, and antioxidants like lutein and zeaxanthin to your meal.

The cheese sauce adds protein and calcium, making this classic zucchini casserole a more substantial side dish. Each serving provides approximately 220 calories with 8 grams of protein.

Seasonal Adaptations

During peak zucchini season, this recipe helps use abundant harvests from gardens and farmers markets. Choose medium-sized zucchini for the best texture, avoiding oversized ones that can be watery and seedy.

You can substitute yellow summer squash for half the zucchini to add color variety without changing the cooking method or timing.

Serving Suggestions

This classic zucchini casserole complements a wide variety of main dishes. Serve alongside roasted chicken, grilled pork chops, or beef tenderloin for elegant dinners. It’s also excellent with simple preparations like baked fish or barbecued meats.

For vegetarian meals, pair with quinoa pilaf or wild rice and a fresh green salad. The rich, cheesy flavors make it substantial enough to serve as a light main course with crusty bread.

Consider this casserole for holiday gatherings, potluck dinners, or meal prep sessions. It travels well and reheats beautifully, making it ideal for busy weeknight dinners when prepared ahead.

Don’t hesitate to experiment with different cheese combinations or add your favorite herbs from the garden. This flexible recipe adapts well to personal preferences while maintaining its classic comfort food appeal.